The interactions and catalyses of various biosubstrates in associated bile salt and bile salt/lipid systems will continue to be investigated, with particular emphasis in the following areas. The role and structures of the free radicals involved in nucleophilic aromatic substitutions in the presence of bile salts will be studied using epr and nmr spectroscopy. Additional studies on the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate anion and other carboxylate anions in the presence and absence of bile salts will be carried out. Drug solubilization and interactions in the presence of bile salt and bile salt/lipid systems will also be investigated using a variety of physical techniques. Studies on the self-association of the sodium salt of glycocholic acid will be carried out by sedimentation equilibrium experiments, and factors influencing it such as temperature and ionic strength will also be done. The interaction of esters of bile acids with cholesterol in chloroform solutions will be studied by vapor pressure osmometry; from studies of this kind, we can determine what type of mixed association is present and how the number of hydroxyl groups affects the interactions. This will also require separate studies on the state of aggregation of the reactants.